In Internet shopping, products handled by a shopping site are displayed to users divided into categories. For example, in Patent Literature 1, an information sending and receiving system for displaying product categories such as “home appliances”, “books” and “computers” on pages listing products is disclosed. A user can easily narrow down products by selecting a category of products they are interested in purchasing from among these categories.
On the other hand, enormous cost is incurred in systematically building and maintaining peculiar expressions such as people's names, place names or product names. Consequently, much research has been conducted on automatic acquisition methods for automatically acquiring by computer the semantic relationship of peculiar expressions. For example, in Non-Patent Literature 1, an algorithm (called the “g-Espresso algorithm”) is disclosed for extracting semantic categories from sentences with words separated by spaces. In addition, in Non-Patent Literature 2, an algorithm (called the “g-Monaka algorithm”) is disclosed for extracting semantic categories from sentences in which words are not separated by spaces.